The occurrence of an unprecedented abundance episode of Historis acheronta semele in July, 2021 in Havana, Cuba is reported. Ecological and ethological notes are made, and the possible causes and outcomes of the presence of large numbers of butterflies in the city are discussed. The absence of additional records makes it impossible to assess if the event is a migration or just a local abundance episode. The event developed during the rainy season of the Cuban climate, in coincidence with previously reported events for similar butterflies in Cuba. Nonetheless, the exact causes of this event remain unknown, as does the host plant of this butterfly in Cuba.